1. Field of the Invention
This invention relates generally to the field of packaged chip integrated optical devices, for chip-integrated infrared optical absorption spectroscopy as well as chip-integrated label-free biomolecule microarray. The apparatus and method enables high throughput sensing as well as high specificity.
2. Background of the Invention
Label-free biosensors are particularly attractive since they avoid complex chemistries caused by steric hindrance of the labels. All methods of detection in lab-on-chip platforms at present transduce the specific binding of the biomolecule of interest to its specific conjugate biomolecule receptor bound to the device substrate, into an electrical, mechanical, or optical signal. Optical detection techniques are generally preferred due to their freedom from electromagnetic interference. While several platforms based on ring resonators, wire waveguides, and surface plasmon resonance (SPR) have been investigated, photonic crystal (PC) microcavities, in general, are more compact (of the order of a few square microns in surface area) and have higher sensitivity than other devices due to slow light effect and the larger optical mode overlap with the analyte within compact optical mode volume. Much of the research in the literature concerns single PC microcavity biosensors. Methods to array two-dimensional PC microcavities have primarily focused on the detection of a single bio-molecular probe binding to its specific conjugate target biomolecule on all microcavities. A method to array photonic crystal microcavities along a single photonic crystal waveguide was previously presented in U.S. Pat. No. 8,293,177. Here, we disclose novel methods to array these PC microcavities using multimode interference optical power splitters which can be combined to create large chip-integrated microarrays in which all PC microcavity sensors, each coated with a different biomolecule target receptor, can be simultaneously interrogated with the same small quantity of probe sample, resulting in high throughout diagnostic assays. The multiplexed detection not only achieves high throughput detection, but the ability to measure many biomolecule interactions at the same instant of time allows one to do the actual test experiments and the control experiments and further multiplex these experiments to achieve higher statistical confidence regarding the specificity of the binding reactions. Sandwich assays can also be performed on the same platform to confirm binding specificity.
In addition, chip integrated optical absorption spectrometers are attractive since they allow chemical and biological analytes to be distinguished on a chip with near-infrared optical absorption signatures. Photonic crystal slot waveguide have been demonstrated as viable agents to perform chip-integrated optical absorption spectroscopy. However, in a photonic crystal slot waveguide, the wavelength range over which light is slowed down as it propagates down the photonic crystal waveguide is small. To increase the wavelength bandwidth over which slow light phenomenon is achieved and thus enable a wide bandwidth, infrared optical absorption spectrometer on chip, it is necessary to multiplex several photonic crystal slot waveguides. A method that couples light into all the photonic crystal slot waveguides simultaneously and thus measures the analyte absorption spectrum across a broad wavelength range on-chip is desired.